1. Field of the Invention
The present disclosure relates to a sheet feeding unit and an image forming apparatus provided with the sheet feeding device and, specifically, to a sheet feeding unit configured to feed sheet separately one by one and an image forming apparatus provided with such a sheet feeding unit.
2. Description of the Related Art
In the related art, image forming apparatuses such as printers, facsimiles, and copying machines configured to store sheets in a feeding cassette demountably mounted on an apparatus body and feed the sheets stored in the feeding cassette separately one by one to an image forming apparatus when forming images are known.
Recently, image forming apparatuses which are reduced in size by bending a sheet feeding path for sheets fed from a feeding cassette significantly upward and feeding the sheets to an image forming unit positioned downstream of the sheet feeding path are proposed. For example, such a technology is disclosed in Japanese Patent Laid-Open No. 01-92148.
In the image forming apparatus configured as described above, separating system such as a separation pad method or a retard method are employed, and a feeding method on the basis of so-called one rotation control, which is control to feed a sheet by a 360-degree rotation of a feeding roller, is employed. In this control, a sheet feeding speed Vp of the feeding roller is set to be higher than a sheet conveyance speed Vf of a conveying roller located downstream. The reason is that if the paper feeding speed of the feeding roller is set to be lower than the sheet conveyance speed of the conveying roller, the feeding roller is pulled by a sheet conveyed by the conveying roller and hence a load is applied to the feeding roller and the conveying roller, so that uneven abrasion on the surfaces of the rollers may result.
When the sheet feeding path is bent significantly upward, a leading edge of the sheet fed from the feeding cassette abuts against the sheet feeding path, and the sheet undergoes a deflection and forms a loop. If the sheet is conveyed by the conveying roller in this state, the loop of the sheet in the sheet feeding path is not eliminated and is further increased because the sheet conveyance speed of the conveying roller is lower than the feeding speed of the feeding roller. If the one rotation control of the feeding roller is employed here, a backward tension is applied from the sheet to the conveying roller and the loop of the sheet in the sheet feeding path is abruptly eliminated when feeding of the sheet by the feeding roller is finished in the state in which the sheet forms the loop. Accordingly, the deflected sheet is pulled and such pulling of the sheet generates a sound.